title: Crosstalk between PI3 kinase/PDK1/Akt/Rac1 and Ras/Raf/MEK/ERK pathways downstream PDGF receptor.
abstract: OBJECTIVE
  Our earlier studies suggested crosstalk between IRS/PI3 kinase/PDK1/Akt/Rac1/ROCK and (Shc2/Grb2/SOS)/Ras/Raf/MEK/ERK pathways downstream PDGF-ββ receptor responsible for chemotaxis and proliferation of malignant mesothelioma cells. The present study was conducted to obtain evidence for this.
  
  
  METHODS
  To assess activation of Akt, MEK, and ERK, Western blotting was carried out on MSTO-211H malignant mesothelioma cells using antibodies against phospho-Thr308-Akt, phopho-Ser473-Akt, Akt, phospho-MEK, MEK, phopho-ERK1/2, and ERK1/2. To knock-down Akt, PI3 kinase, PDK1, and Rac1, siRNAs silencing each-targeted gene were constructed and transfected into cells. To monitor Rac1 activity, FRET monitoring was carried out on living and fixed cells.
  
  
  RESULTS
  ERK was activated under the basal conditions in MSTO-211H cells, and the activation was prevented by inhibitors for PI3 kinase, PDK1, Akt, and Rac1 or by knocking-down PI3 kinase, PDK1, Akt, and Rac1. Akt was also activated under the basal conditions, and the activation was suppressed by a MEK inhibitor and an ERK1/2 inhibitor. In the FRET analysis, Rac1 was activated under the basal conditions, and the activation was inhibited by a MEK inhibitor and an ERK1/2 inhibitor.
  
  
  CONCLUSIONS
  The results of the present study show that ERK could be activated by PI3 kinase, PDK1, Akt, and Rac1 and that alternatively, Akt and Rac1 could be activated by MEK and ERK in MSTO-211H cells.
authors.affiliation: Division of Bioinformation, Department of Physiology, Hyogo College of Medicine, Nishinomiya, Japan.
authors.forename: Emma Tabe Eko
authors.initials: ET
authors.lastname: Niba
authors.forename: Hisao
authors.initials: H
authors.lastname: Nagaya
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kanno
authors.forename: Ayako
authors.initials: A
authors.lastname: Tsuchiya
authors.forename: Akinobu
authors.initials: A
authors.lastname: Gotoh
authors.forename: Chiharu
authors.initials: C
authors.lastname: Tabata
authors.forename: Kohzo
authors.initials: K
authors.lastname: Kuribayashi
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakano
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Nishizaki
mesh_terms: D045744:Cell Line, Tumor; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D020930:MAP Kinase Kinase Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D058539:Phosphatidylinositol 3-Kinase / Q000235:genetics / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism*; D015398:Signal Transduction; D020830:rac1 GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D048490:raf Kinases / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism
chemical_list: C000631429:PDK1 protein, human; D000081082:Phosphoinositide-3 Kinase Inhibitors; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D058539:Phosphatidylinositol 3-Kinase; D017479:Receptors, Platelet-Derived Growth Factor; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D048490:raf Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020930:MAP Kinase Kinase Kinases; D020830:rac1 GTP-Binding Protein; D018631:ras Proteins